The present invention relates to a method of manufacturing a hollow plastic ball including the steps of, introducing polyvinyl chloride resin paste in a metal mold to form the hollow ball, and gelating said resin paste along the inner surface of the metal mold. More particularly, the present invention relates to the improvement in the manufacture of an inlaid hollow plastic ball.
It is well known to manufacture the above-mentioned hollow ball by gelation of a polyvinyl chloride resin paste in a mold while heating and rotating the mold laterally and lengthwise.
One of the known processes of applying a decorative figure or pattern on the surface of a hollow ball is to paint or print the desired figure or pattern on the thus-produced hollow ball. However, these figures or patterns must be individually hand-painted and therefore such method is not suitable to mass production. Moreover, the printed image is easily erased or separated from the surface so that the decoration is only temporary. Further, paint or printing ink is not suitable because when such decorative objects are designed for the amusement of babies, the removable ink or paint may be harmful to the baby.
One of the known processes to overcome some of these disadvantages is to form a half-gelated film on the inner surface of the mold by heating a portion of the polyvinyl chloride resin paste, to paint the desired figure by handwriting on the film, and to gelate the remainder of the polyvinyl chloride resin paste in the mold. Thus, a hollow plastic ball having an inlaid figure or pattern in the surface layer of the ball is obtained. However, this process is complex and hand-writing on the concave inner surface is more difficult, so that the process also cannot be adopted for mass production, although a rather permanent and harmless image can be produced by this method.